1. Field of the Invention
The present invention relates to a radiation image storage panel employable for a radiation image recording and reproducing method utilizing a stimulable phosphor.
2. Description of the Prior Art
For obtaining a radiation image, there has been conventionally employed a radiography utilizing a combination of a radiographic film having an emulsion layer containing a photosensitive silver salt material and an intensifying screen. As a method replacing the conventional radiography, a radiation image recording and reproducing method utilizing a stimulable phosphor as described, for example, in U.S. Pat. No. 4,239,968, has been recently paid much attention. In the radiation image recording and reproducing method, a radiation image storage panel comprising a stimulable phosphor (i.e., a stimulable phosphor sheet) is used, and the method involves steps of causing the stimulable phosphor of the panel to absorb a radiation energy having passed through an object or having radiated from an object; sequentially exciting the stimulable phosphor with an electromagnetic wave such as visible light and infrared rays (hereinafter referred to as "stimulating rays") to release the radiation energy stored in the phosphor as light emission (stimulated emission); photoelectrically detecting the emitted light to obtain electric signals; and reproducing the radiation image of the object as visible image from the electric signals.
In the radiation image recording and reproducing method, a radiation image is obtainable with a sufficient amount of information by applying a radiation to an object at considerably smaller dose, as compared with the conventional radiography. Accordingly, this method is of great value especially when the method is used for medical diagnosis.
The radiation image storage panel employed in the radiation image recording and reproducing method has a basic structure comprising a support and a phosphor layer provided on one surface of the support. Further, a transparent film of a polymer material is generally provided on the free surface (surface not facing the support) of the phosphor layer to keep the phosphor layer from chemical deterioration or physical shock.
The phosphor layer comprises a binder and a stimulable phosphor dispersed therein. The stimulable phosphor emits light (gives stimulated emission) when excited with an electromagnetic wave such as visible light or infrared rays (stimulating rays) after having been exposed to a radiation such as X-rays. Accordingly, the radiation having passed through an object or having radiated from an object is absorbed by the phosphor layer of the radiation image storage panel in proportion to the applied radiation dose, and a radiation image of the object is produced in the panel in the form of a radiation energystored image. The radiation energy-stored image can be released as stimulated emission by sequentially irradiating the panel with stimulating rays. The stimulated emission is then photoelectrically converted to electric signals, so as to reproduce a visible image from the electric signals.
The radiation image recording and reproducing method is a very advantageous method for obtaining a visible image as described above, and a radiation image storage panel employable in the method is desired to have high sensitivity and provide an image of high quality (high sharpness, high graininess, etc.) as well as a radiographic intensifying screen employed in the conventional radiography. Particularly when the method is applied to medical radiography, the sensitivity of the radiation image storage panel is desired to have higher level even if the level-up is little, from the viewpoint of lowering the radiation dose applied to a human body.
Further, in the case that the stimulable phosphor contained in the phosphor layer is liable to be deteriorated through the environmental atmosphere, for instance, that the phosphor is decreased in the emission luminance by absorption of water (namely, the phosphor lacks water vapro resistance), it is desired to prevent the stimulable phosphor from the deterioration (and to prevent the panel from decrease of sensitivity) by making the phosphor particles water vapor-resistant.